This invention relates to an electronic traction control system for an articulated work machine and, more specifically, to an electronic control system which brakes each wheel independently and at least partially bases the brake control on the rate of articulation of the work machine.
Work machines used at construction sites and other off-road locations are often four wheel drive articulated machines. An articulated machine includes front and rear frames hinged together by an articulation joint for relative pivotal movement. When one of the frames is moved relative to the other, the machine turns. The articulation joint also moves back and forth in a known manner perpendicular to a centerline of the machine as the machine articulates, imparting an additional component of motion to the machine""s turning dynamics.
Sometimes such work machines experience a loss of traction, often due to poor underfoot conditions or a change in the weight distribution of the machine. Traction loss events may also occur when one wheel of the machine spins at a very different speed than the other wheels, because that wheel is stuck in one position (therefore not spinning) or is spinning uncontrollably because the tread of the wheel cannot grip the ground. This slipping and subsequent loss of traction is undesirable in that the machine works less efficiently when slipping, and the ground surface under the machine can become rutted and damaged. The tire or wheel of the machine can also suffer physical damage or thermal wear if the wheel slips or skids.
Various mechanical traction solutions have been developed and placed in commercial use. For example, one method to prevent front or rear wheel slip involves locking the differential on the slipping axle. However, since the differential operation is then restrained and not controlled responsive to some sensed factor, the wheels are held to the same speed and articulation may be adversely effected. Some difference in left/right wheel speed is needed for the front and rear frames to articulate in an optimal manner to turn the machine.
Articulated work machines are often provided with a separately actuable brake for each wheel. These brakes can be actuated manually or automatically as needed to bring a free-spinning wheel under control, much as the automobile driver taps the brake pedal to restore traction, albeit with much more precise control.
An automatic traction control system used to actuate brakes individually is disclosed in U.S. Pat. No. 5,535,124, issued Jul. 9, 1996 to Javad Hosseini et al. (hereafter referenced as ""124). The traction control system of ""124 detects the difference in rotational velocity between the two wheels of the front or rear frame, detects the articulation angle of the machine (an articulation angle of zero means that the machine is not being turned), and then responsively produces a braking control signal to slow the faster rotating wheel. The ""124 braking control signal takes into account the fact that one of the wheels may need to rotate more quickly if it is the outer wheel and weights the braking control signal accordingly.
The ""124 traction control system, however, calculates the braking control signal using a desired speed ratio between each set of inner and outer wheels. The ratio can falsely indicate that the wheels are not slipping when there actually is a loss of traction. Missed traction events often occur if, for example, both inner and outer wheels are slipping slightly, or only the inner wheel is slipping, since the controller only checks to see if the ratio of the faster wheel speed to the slower wheel speed is greater than expected, thus ignoring the absolute wheel speeds. Also, the ""124 system does not take into account the effect of the back-and-forth, or lateral, movement of the articulation joint during articulation. The portion of the wheel speed attributed to the articulation rate and the lateral movement of the articulation joint is not insignificant and can mask small losses of traction, leading the ""124 traction control system to miss the wheel slipping events. Finally, the ""124 system does not consider the effect of the load carried by the machine and how that load causes one or more wheels of the machine to be slightly more or less likely to slip.
The present invention is directed to overcoming one or more of the problems as set forth above.
In a preferred embodiment of the present invention, an electronic traction control system for a work machine is disclosed. The work machine has a front frame, a rear frame, and an articulation joint connecting the front and rear frames. The system includes an articulation sensor, at least two wheels, a brake associated with the work machine, and an electronic control module. The articulation sensor is adapted to provide an articulation angle signal. Each wheel is adapted to provide a wheel speed signal. The electronic control module is adapted to receive the articulation angle and wheel speed signals; calculate an articulation rate responsive to the articulation angle signal; determine a desired wheel speed having at least one of: an articulation-caused linear velocity component calculated responsive to the articulation rate, articulation angle, and wheel speed signals, and a transient articulation-caused velocity component calculated responsive to the articulation rate, articulation angle, and wheel speed signals; and responsively produce a brake signal to control the brake.
In a preferred embodiment of the present invention, an electronic traction control system for a work machine is disclosed. The work machine has front and rear frames connected by an articulation joint for relative pivotal movement. Each frame has at least one driven wheel. The electronic traction control system includes an articulation sensor associated with the articulation joint and adapted to produce an articulation angle signal, a wheel speed sensor associated with each wheel and adapted to produce a wheel speed signal, and an electronic control module. The electronic control module is adapted to receive the articulation angle signal and the wheel speed signals, determine a measured wheel velocity value responsive to each wheel speed signal, determine an articulation rate value responsive to the articulation angle signal, calculate an articulation-caused linear velocity value for each wheel responsive to the articulation angle, articulation rate, and wheel speed signals and a transient articulation-caused velocity value for each wheel responsive to the articulation angle, articulation rate, and wheel speed signals, calculate a desired wheel velocity value for each wheel responsive to the articulation-caused linear velocity value and the transient articulation-caused velocity value, calculate an error value responsive to the measured wheel velocity value and the desired wheel velocity value, and produce a brake signal for each wheel responsive to the error value. The electronic control system also includes a brake associated with each wheel, adapted to receive the brake signal and actuate responsively thereto.
In a preferred embodiment of the present invention, a method of controlling wheel slip of an articulated work machine is disclosed. The method includes the steps of: comparing the relative positioning of a front frame and a rear frame of the work machine and responsively producing an articulation angle signal; sensing a speed of at least one wheel associated with at least one of the front and rear frames and responsively producing a wheel speed signal; receiving the articulation angle signal and each wheel speed signal; producing a wheel speed value responsive to each wheel speed signal; and determining a rate of change of the articulation angle signal and responsively producing an articulation rate value. The method also includes: producing an articulation-caused linear velocity value responsive to the articulation angle signal, the articulation rate value, and each wheel speed signal; producing a transient articulation-caused velocity value responsive to the articulation angle signal, the articulation rate value, and each wheel speed signal; and producing a desired wheel speed value based on the articulation-caused linear and transient articulation-caused velocity values. Additionally, the method includes: comparing the wheel speed value to the desired wheel speed value; producing a brake signal responsive to the difference between the actual wheel speed value and the desired wheel speed value; and controlling a brake associated with each wheel responsive to the brake signal.